Array.prototype.myMap = function (cb, thisArg) {
    const newArr = []
    for (let i = 0; i < this.length; i  ) {
        if (i in this) {
            newArr[i] = cb.call(thisArg, this[i], i, this)
        }
    }
    return newArr
}

Array.prototype.myMap = function (cb, thisArg) {
    const newArr = []
    const len = this.length
    for (let i = 0; i < len; i  ) {
        if (i in this) {
            newArr[i] = cb.call(thisArg, this[i], i, this)
        }
    }
    return newArr
}

whth the "i < this.length" I don't know why isn't pass any test case ,It's show infinite always

CodePudding user response：

These will be different if the callback function modifies the length of the array being iterated over. For instance:

[1, 2, 3].myMap((el, index, array) => {
    array.push(0);
    return el   1;
});

The second version will never end because this.length keeps increasing as the loop continues. But the first version just processes the original 3 elements of the array.